Voltage Controlled Oscillators (VCOs) are an integral part of the frequency reference circuitry in transmitters and receivers producing the carrier waves which are modulated by the information being conveyed in telecommunications equipment. In prior art, the power supplies for the VCOs would be voltage or current sources. As tolerances for electrical components of an integrated circuit process increase, the variation in the performance of a VCO increases, often causing it to miss critical performance specifications when mass produced. To mitigate the variation, the VCO's power supply is sometimes made programmable so that it can be adjusted as the frequency of the VCO is changed or its operating temperature changes. In some prior art, a duplicate circuit of the VCO's active components is used in an attempt to mirror the behavior of the VCO, so that the VCO's power supply can be adjusted based on the variation of those active devices. The limitations of these approaches are that they cannot mirror the actual performance of the VCO since the VCO is oscillating. An oscillating circuit has characteristics associated with the quality, or Q, factor of its resonator that vary with tolerances, and which are not reflected by simple active devices or programmable sources. Creating a duplicate oscillating circuit to mirror the behavior of the VCO would create a frequency that would interfere with the frequency of the VCO itself, causing spurs. Therefore, these prior art approaches will not fully compensate for the variation in the VCO due to tolerances.